Companies with a financial interest in a weed-killer sometimes found in drinking water paid for thousands of studies federal regulators are using to assess the herbicide’s health risks,records of the U.S. Environmental Protection Agency show. Many of these industry-funded studies, which largely support atrazine’s safety, have never been published or subjected to an independent scientific peer review.

Meanwhile, some independent studies documenting potentially harmful effects on animals and humans are not included in the body of research the EPA deems relevant to its safety review, the Huffington Post Investigative Fund has found. These studies include many that have been published in respected scientific journals.

Even so, the EPA says that it would be “very difficult for someone to put a thumb on the scale” to slant the outcome.

Atrazine is one of the most widely used herbicides in the U.S. An estimated 76 million pounds of the chemical are sprayed on corn and other fields in the U.S. each year, sometimes ending up in rivers, streams, and drinking water supplies. It has been the focus of intense scientific debate over its potential to cause cancer, birth defects, and hormonal and reproductive problems. As the Huffington Post Investigative Fund reported in a series of articles last fall, the EPA failed to warn the public that the weed-killer had been found at levels above federal safety limits in drinking water in at least four states. Some water utilities are suing Syngenta to have it pay their costs of filtering the chemical.

Now the EPA is re-evaluating the health risks of atrazine, which was banned in the European Union in 2004 due to a lack of evidence to support its safe use. That ban includes Switzerland, where atrazine’s manufacturer, Syngenta, is headquartered. The EPA expects to announce results of its re-examination of the herbicide in September 2010. It could take action ranging from restrictions on its use on crops to an outright ban. Or it could permit continued use without additional restrictions.

The company, one of the world’s largest agribusinesses, says the chemical has been used safely for decades and restrictions could prove devastating to farmers who are heavily dependent on the inexpensive herbicide. Atrazine poses “no harm” to the general population or to drinking water supplies, said company spokesman Steven Goldsmith.

EPA records obtained by The Huffington Post Investigative Fund show that at least half of the 6,611 studies the agency is reviewing to help make its decision were conducted by scientists and organizations with a financial stake in atrazine, including Syngenta or its affiliated companies and research contractors.

More than 80 percent of studies on which the EPA are relying have never been published. This means that they have not undergone rigorous “peer review” by independent scientists, a customary method to ensure studies are credible and scientifically sound before they can be published in major journals.

At the same time several prominent studies by independent academic scientists in well-respected scientific journals – showing negative reproductive effects of atrazine in animals and humans – are absent from the EPA’s list.

That finding may raise concerns about how the agency is doing its work. Rep. Henry Waxman, chairman of the House Energy and Commerce Committee, which oversees environmental regulators, told the Investigative Fund, “it’s critically important that EPA use all of the information at its disposal.”

Agency scientists may review studies not on the list, but EPA senior policy analyst William Jordan said that the 6,611 studies are those considered “relevant to the assessment of atrazine.”

‘Not Just Atrazine’

EPA spokeswoman Betsaida Alcantara said the list was not exhaustive and that some studies may not be on the list because they were not given an eight-digit “master record identification number,” which the agency uses to keep track of studies. There is “no uniform practice” for assigning numbers to studies submitted by people other than those working for herbicide, fungicide or pesticide manufacturers, she added.

EPA officials said that with a limited budget the agency must rely heavily on research sponsored by parties with a stake in the outcome. The agency’s “test guidelines” governing how experiments are conducted – the types and number of lab animals to be used, for instance. These provide sufficient safeguards against skewed results, officials said.

“Companies have a very strong incentive to follow the guidelines,” said EPA senior analyst Jordan. “We hope and think that we have written the guidelines with enough detail that it would be very difficult for someone to put a thumb on the scale, as it were, to slant the outcome, [or] to make something look safer than it is.”

Jennifer Sass, a senior scientist specializing in health issues at the Natural Resources Defense Council, argues that relying on a company to test the safety of its own product – an “inherent conflict” of interest – is part of a larger pattern at the EPA. “It’s not just happening with atrazine,” she said.

Hundreds of herbicides, pesticides, and other chemicals are regulated by the EPA, whose decisions can have significant implications for public health and on the abilities of an array of multinational companies to earn billions of dollars in the U.S.

By law, industry influence often is built into the regulatory process of the federal government. At the Food and Drug Administration, for instance, clinical trials conducted by pharmaceutical companies are used to determine whether pills and devices work and are safe. Makers of pesticides, herbicides, and fungicides also must pay for studies on their products. Ifthey meet agency rules for conducting the testing, the EPA must accept them.